I have a similar setup. I think I understand your last post but a drawing would be better to understand what you are trying to do. On my system, I have a traditional dual Cessna switch that control 2 separate batteries, a separate switch that turns on and off my back up battery for the G3X system and an alternator switch. The backup battery switch is the first thing I turn on and the last thing that I turn off. It needs to be On to re-charge the backup battery (at least in my set up it does). The only thing I will emphasize is this, if I'm understanding you correctly you want the switch to be OFF and for it to still work as outlined above... It needs to be On for it work this way and also to charge the backup battery... otherwise, why would you even have a switch to the backup battery?

I have a similar setup. I think I understand your last post but a drawing would be better to understand what you are trying to do. On my system, I have a traditional dual Cessna switch that control 2 separate batteries, a separate switch that turns on and off my back up battery for the G3X system and an alternator switch. The backup battery switch is the first thing I turn on and the last thing that I turn off. It needs to be On to re-charge the backup battery (at least in my set up it does). The only thing I will emphasize is this, if I'm understanding you correctly you want the switch to be OFF and for it to still work as outlined above... It needs to be On for it work this way and also to charge the backup battery... otherwise, why would you even have a switch to the backup battery?

I stink at drawings. Maybe I stink at descriptions, too. The switch would have three positions. From bottom to top, they would be: OFF, which disconnects both the master and the backup battery. BACKUP, which connects only the backup battery. And MAIN, which connects both the backup battery and the main battery. It would not be possible to turn the backup battery off while the main battery is on. It would be possible to turn the main battery off while the backup battery is on.

But the point immediately below yours is quite valid: In turbulence, it would be quite easy to accidentally push the switch full down and shut off the entire airplane while trying to switch to backup power in the event of a main power bus failure. Separate switches are probably safer for that reason. In my plane, when all else is equal, safety makes the decision.

Like I'd mentioned in my previous post, check out the Honeywell 2TL1-31 switch. It's a very heavy duty double pole/three position switch with a lockout preventing you from inadvertently moving the switch into the off position, but it can easily be toggled between positions two and three. I'll defer to the rest of the experts with regards to your overall architecture of your switchology the do's and don'ts, but this Honeywell switch with the lockout might just do the trick and accomplish what you're trying to do.

Like I'd mentioned in my previous post, check out the Honeywell 2TL1-31 switch. It's a very heavy duty double pole/three position switch with a lockout preventing you from inadvertently moving the switch into the off position, but it can easily be toggled between positions two and three. I'll defer to the rest of the experts with regards to your overall architecture of your switchology the do's and don'ts, but this Honeywell switch with the lockout might just do the trick and accomplish what you're trying to do.

Mark

Thanks for the part number suggestion. Switch part numbers are always fun to look through because there are a million different configurations. Honeywell's document about the TL series is no different.

Most likely I will simplify this to separate switches, but anywhere that I do use a 3-position switch, I now know that there are lockout switches available to use.

Thanks for the part number suggestion. Switch part numbers are always fun to look through because there are a million different configurations. Honeywell's document about the TL series is no different.

Most likely I will simplify this to separate switches, but anywhere that I do use a 3-position switch, I now know that there are lockout switches available to use.

Yeah, that same Honeywell 2TL1- switch comes in about ten different configurations based on lockout position or no lockout at all, momentary or not, all three positions on, one position off, etc. etc. The last number that you put in after dash (2TL1-?) determines the configuration. Here's their pdf brochure of all their toggle switches and all of the different configurations that you can get them in. https://sensing.honeywell.com/honeyw...05430-3-en.pdf You just need study them a little bit to make sure you're getting the configuration that you want. There’s quite a few places online that you can order them from.

Yeah, that same Honeywell 2TL1- switch comes in about ten different configurations based on lockout position or no lockout at all, momentary or not, all three positions on, one position off, etc. etc. The last number that you put in after dash (2TL1-?) determines the configuration. Here's their pdf brochure of all their toggle switches and all of the different configurations that you can get them in. https://sensing.honeywell.com/honeyw...05430-3-en.pdf You just need study them a little bit to make sure you're getting the configuration that you want. There’s quite a few places online that you can order them from.

Here at SteinAir, the combination we see most often is a Master switch for the primary battery and primary alternator, usually the aforementioned locking toggle, which we stock at SteinAir. If needed, we add a second switch for a second alternator field and if there are two batteries and they are not in parallel, another battery switch and a second contactor. With two separate batteries things get complicated so I won't go into that here. If you have two alternators we advocate running them both at the same time, with the backup alternator regulated .5 volt or so lower than the primary. The backup will then "idle" with little or no excitation until the bus voltage drops below it's regulated value. It will then pick up the load, and if you set an alert between the primary and backup voltage your EFIS can show "Primary Alt Fail" or something similar. There is absolutely no point in leaving a second alternator turned off in flight.
If you have an avionics backup battery such as TCW's IBBS, the drill is usually to turn it to the On or Armed position first, make sure it powers the connected items. Then you proceed with the normal power-up and start procedure. The IBBS will also prevent an EFIS reboot ("brownout") during engine cranking. The IBBS switch stays in ON or Arm for the whole flight. There is also no point in trying to run the IBBS at the same time the main battery/alternator is powering the bus, as it only comes on when the bus voltage is low. The idea is to use the main battery first, then the IBBS. Our EFIS systems only draw about 7-9 amps when fully powered so between the main battery and the IBBS you can fly a long time and still have your EFIS and EMS.

Here at SteinAir, the combination we see most often is a Master switch for the primary battery and primary alternator, usually the aforementioned locking toggle, which we stock at SteinAir. If needed, we add a second switch for a second alternator field and if there are two batteries and they are not in parallel, another battery switch and a second contactor. With two separate batteries things get complicated so I won't go into that here. If you have two alternators we advocate running them both at the same time, with the backup alternator regulated .5 volt or so lower than the primary. The backup will then "idle" with little or no excitation until the bus voltage drops below it's regulated value. It will then pick up the load, and if you set an alert between the primary and backup voltage your EFIS can show "Primary Alt Fail" or something similar. There is absolutely no point in leaving a second alternator turned off in flight.
If you have an avionics backup battery such as TCW's IBBS, the drill is usually to turn it to the On or Armed position first, make sure it powers the connected items. Then you proceed with the normal power-up and start procedure. The IBBS will also prevent an EFIS reboot ("brownout") during engine cranking. The IBBS switch stays in ON or Arm for the whole flight. There is also no point in trying to run the IBBS at the same time the main battery/alternator is powering the bus, as it only comes on when the bus voltage is low. The idea is to use the main battery first, then the IBBS. Our EFIS systems only draw about 7-9 amps when fully powered so between the main battery and the IBBS you can fly a long time and still have your EFIS and EMS.

Just saw your post today. Thanks for posting it. What is odd to me is to see planes with the IBBS switch located in such a place on the panel that it is not a smooth flow to turn that on as step 1 in the before engine start checklist, as it seems it ought to be.

The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.